The present invention relates to a liquid crystal device having a novel addressing technique. The invention also relates to a method of addressing a liquid crystal device and to an arrangement for addressing a liquid crystal device.
In a liquid crystal device array there are typically a first set of electrodes (or row electrodes) arranged on a first substrate of the device and a second set of electrodes (or column electrodes) arranged on an opposite substrate of the device. These sets of electrodes generally comprise electrodes arranged parallel to one another but at right angles to the electrodes in the other set. The intersection between a row electrode and a column electrode defines a picture element or pixel of the array. Each pixel of the array can be uniquely addressed by applying a scanning signal to each of the row electrodes in turn, while a data signal is applied to each of the column electrodes. The data and scanning signals must be carefully selected so that only those pixels in the row to which the scanning signal is applied will adopt the state as a consequence of the data signal. Once a scanning signal has been applied to all of the row electrodes, the process can start again with potentially different data signals applied.
The scanning signal typically comprises a blanking pulse and a strobe pulse. The blanking pulse operates independently of the data signal to place all of the pixels in a particular row in a known state (typically the black state). Once the blanking pulse has altered the state of any pixels in the row which have previously occupied the other state, a strobe pulse is applied to the row electrode simultaneously with a data signal. The data signal may be selected from two or more possible data signals to place the pixel in the desired state.
The data signals are applied to the second plurality (column) electrodes continuously and thus cause both device heating and a reduction in contrast of the display.
It is an object of the present invention to provide an addressing technique for liquid crystal devices that ameliorates these disadvantages.
According to a first aspect of the present invention there is provided a method of addressing a liquid crystal device having a first plurality of electrodes and a second plurality of electrodes defining a plurality of pixels at the intersections between at least one of the first plurality of electrodes and at least one of the second plurality of electrodes, the method comprising applying a scanning signal including at least one strobe portion to each of the first plurality of electrodes over a frame, applying data signals to each of the second plurality of electrodes to cooperate with the at least one strobe portion of the scanning signal, wherein the scanning signal further comprises an alternating signal having a frequency greater than the frame rate and less than or equal to the lowest possible frequency applied to the device by the data signals.
According to a second aspect of the present invention there is provided a liquid crystal device having a first plurality of electrodes and a second plurality of electrodes defining a plurality of pixels at the intersections between at least one of the first plurality of electrodes and at least one of the second plurality of electrodes, further comprising means for applying one frame of a scanning signal including at least one strobe portion to each one of the first plurality of electrodes, means for applying data signals to each of the second plurality of electrodes to cooperate with the at least one strobe portion of the scanning signal, wherein the scanning signal further comprises an alternating signal having a frequency greater than the frame rate and less than or equal to the lowest possible frequency applied to the device by the data signals.
According to a third aspect of the present invention there is provided an addressing arrangement for a liquid crystal device having a first plurality of electrodes and a second plurality of electrodes defining a plurality of pixels at the intersections between at least one of the first plurality of electrodes and at least one of the second plurality of electrodes, the arrangement comprising means for applying one frame of a scanning signal including at least one strobe portion to each one of the first plurality of electrodes, means for applying data signals to each of the second plurality of electrodes to cooperate with the at least one strobe portion of the scanning signal, wherein the scanning signal further comprises an alternating signal having a frequency greater than the frame rate and less than or equal to the lowest possible frequency applied to the device by the data signals.
The invention operates by applying a low frequency signal to the row electrodes of the array. This results in a smaller difference in contrast between extreme addressing scenarios and reduced power consumption. The invention may be applied to an addressing scheme using bipolar strobe portions or to an addressing scheme using blanking portions.
Since most of the power consumption comes from the data signal, a reduction in the data signal significantly reduces the power consumption. However, the voltage level of the data signal provides addressing discrimination and the AC stabilization effect, and therefore the invention resides in the addition of an AC signal to the scanning signal to recover AC stabilization and also make the effect more data pattern independent. In order to achieve such data pattern independence (and also so as not to insignificantly increase power consumption) the AC signal applied should be of relatively low frequency and related to the data frequency.
Further preferred features of the invention are set out in the dependent claims and will be apparent to the skilled person on reading the following description.
The present invention will now be described by way of example with reference to the accompanying drawings.